A. Field of the Invention
This invention relates to a broad band frequency divider using varactor diodes which operate at microwave frequencies.
B. Description of the Prior Art
The existing literature on varactor diode frequency dividers is mainly concerned with their use as computer logic elements. The basic patent is U.S. Pat. No. 2,815,488 which issued to Von Neumann on 3 Dec., 1957. However, this patent deals with a lumped circuit realization of a subharmonic generator. Furthermore, Von Neumann's application is not for broad band frequency dividers but rather for the use of a subharmonic generator as a computer element. In addition, Von Neumann contemplates operating the nonlinear device in a small signal fashion about its equilibrium state.
A microstrip subharmonic generator using a single varactor diode was described by Sterzer in "Microwave Parametric Subharmonic Oscillators For Digital Computing", Proceedings of the IRE, Volume 47, No. 8, August 1959, pages 1317-1324. In this reference, the input and output frequencies were 4 GHz and 2 GHz which are less than the frequencies encountered in the invention described herein. Also, the bandwidth was not reported. Sterzer's circuit has an output signal which contains harmonics of all orders of the desired output signal. The present invention eliminates this last problem substantially.
Onyshkevych, Kosonocky and Lo described a varactor diode subharmonic generator in the same frequency range as Sterzer and achieved an octave bandwidth. Again, a computer application was the purpose of this investigation which is reported in an article entitled "Parametric Phase-Locked Oscillator -- Characteristics and Applications to Digital Systems", IRE Transactions on Electronic Computers, Volume EC-8, No. 3, September 1959, pages 277-286.
Finally, the inventor (as mentioned hereinafter) performed a theoretical analysis of a lumped element version of a broad band frequency divider in "Steady-State and Transient Phenomenon in Parametric Subharmonic Oscillators" a Doctoral Thesis by R. G. Harrison for the Imperial College of Science and Technology, University of London, London, England in July, 1964. The inventor also reported the experimental results of an investigation into the steady-state and transient behaviour of two different types of subharmonic oscillator in the above-mentioned reference. However, microwave frequency ranges were not contemplated.